Even though the boiler serial and Gas Council numbers for an appliance don't appear on any certificates, it's an easy process to locate these fields within the software.
Using the Website
Head to the Job Addresses tab on the website and select the property.
Tap on the "Gas Appliances" button to show all appliances at this address
Click the appliance to show it's information, including the Serial/Gas Council numbers.
Using the App
Tap "Job Addresses" from the main menu, find and select the address.
Scroll to the bottom of the page and tap on "Gas Appliances", then tap on the appliance itself to show it's information, including Serial/Gas Council numbers